1) Field of the Invention
The invention relates to a process for preparing vinyl ester or vinyl ester-ethylene polymers in the form of their aqueous dispersions, and also to the use of the resultant dispersions as adhesives or textile binders.
2) Background Art
Aqueous synthetic resin dispersions and corresponding powders have for many years been indispensable additives for applications in the construction sector, for example for renders, mortars, reinforcement compositions, self-leveling compositions, tile adhesives, paints and composite thermal insulation systems. Especially for high-quality renders, there is constantly increasing use of binders which give properties such as better mechanical properties, better weathering resistance and lower susceptibility to soiling.
When highly hydrophobic properties are to be achieved, but with good water vapor permeability, as is the case with silicate renders, use is frequently made of synthetic resins made from hydrophobic monomers, such as vinyl chloride or styrene/butyl acrylate. Vinyl chloride is particularly attractive on cost grounds and its use has been popular in the past. For environmental reasons it is now undesirable. In addition, renders formulated with binders comprising vinyl chloride are highly sensitive to other additives required, such as thickeners or antifoams, and this means that the good hydrophobic properties are often lost when mixing specifications change, for example when there is a change in the type of antifoam. EP-A 217380 (U.S. Pat. No. 4,748,202), for example, describes dispersions comprising VC which are polymerized in the presence of a protective colloid that becomes completely dissolved during the polymerization.
WO 94/20556 (U.S. Pat. No. 5,708,093) recommends copolymerization of silanes to improve wet adhesion and to hydrophobicize aqueous coating compositions. The silanes are incorporated into the shell of core-shell polymers. A disadvantage here is the reduction in storage stability resulting from the incorporation of silane units.
EP-A 338486 describes a process for preparing core-shell polymers where these polymers are non-silanized and are prepared in the presence of a water-soluble protective colloid. The protective colloids used are very low-molecular-weight polymers which become completely dissolved during the polymerization. These dispersions are unsuitable for hydrophobicization in construction applications, because they do not give a lasting hydrophobicization independent of the mixing specification.
The object of the invention was to develop a dispersion which is attractive on cost grounds, environmentally accepted, i.e. free of vinyl chloride, and resistant to freezing and thawing, and whose properties in building applications, for example renders, are good and comparable with those of the vinyl chloride dispersions used hitherto, and which also has the advantage that the hydrophobic properties of the render formulation are less sensitive to changes within the other components.